Direct laryngoscopy (DL) is the most common technique for tracheal intubation in the emergency setting. In experienced hands, DL has a very high success rate, and the equipment is inexpensive, reliable, and widely available. However, DL requires significant experience to gain proficiency and has inherent limitations that manifest when factors such as decreased cervical mobility, a large tongue, a receding chin or prominent incisors are present.

The concept of DL is simple—to create a straight line of site from the mouth to the larynx in order to visualize the vocal cords. The tongue is the greatest obstacle to laryngoscopy. The laryngoscope is used to control the tongue and displace it out of the line of sight. A laryngoscope consists of a handle, a blade, and a light source. It is a left-handed instrument despite the operator’s handedness. In general, DL blades are either curved (Macintosh) or straight (Miller) (Fig. 12-1). Both blades come in a variety of sizes from newborn to large adult, and sizes 3 and 4 are commonly used in adults. Macintosh blades have a gentle curve, a vertical flange for displacing the tongue and a relatively wide square tip with an obvious knob. Variations of the original Macintosh blade design, which include a smaller vertical flange and a shorter light-to-tip distance have also been manufactured. The vertical flange height of the size 3 and 4 blades is similar making it reasonable to start with the longer size 4 blade in all adults. Curved blades are intended to be advanced into the vallecula and when the knob on the tip makes contact and depresses the hyoepiglottic ligament, the epiglottis elevates exposing the vocal cords (Fig. 12-2).

Miller blades have a narrower and shorter flange and a slightly curved tip without a knob. The smaller flange may be advantageous when there is less mouth opening, but makes tongue control more difficult and decreases the area of displacement for visualization and tube placement. Size 3 and 4 Miller blades are nearly identical except for length, so it may be reasonable to start with the longer size 4 blade in most adults. Miller blades are intended to be passed posterior to the epiglottis, to lift it directly
in order to expose the vocal cords (Fig. 12-3). Most operators prefer the curved Macintosh blade because it is wider and allows better control of the tongue; however, the straight Miller blade may provide better visualization of the glottis when there is limited cervical movement, prominent upper incisors, a large tongue, limited mouth opening, or a floppy epiglottis, so it is important to master both techniques.

Recognition of anatomic landmarks is critical to DL success (See Figs 12-4 and 4-5 pages 124 and 41, respectively.) For laryngoscopy the most important laryngeal structures are the epiglottis, the posterior arytenoid cartilages and interarytenoid notch, and the vocal cords. Tracheal intubation is accomplished by passing the endotracheal tube (ETT) through the vocal cords. Success is more likely if the vocal cords are well visualized; however, tracheal intubation does not always require visualization of the vocal cords. If only the posterior cartilages are visible, the tube can be passed anterior to these structures in the midline and will usually enter the trachea (Fig. 12-4B). Furthermore, intubation can often be accomplished when the only visible structure is the epiglottis (Fig. 12-4C), especially if an endotracheal tube introducer (ETI or “bougie”) is used. If the epiglottis cannot be identified, the likelihood of successful tracheal intubation is very low (Fig. 12-4D).

Before embarking on the intubation attempt, the airway manager must ensure that the following are available:

The assistant should be prepared to do the following:

Preintubation assessment of the patient’s airway is essential and must be performed on every patient before administration of neuromuscular blockers. In the mnemonic LEMON, discussed in Chapter 2, the M stands for Mallampati, serving as a reminder to examine the oral cavity to assess the relative size of the tongue in relationship to the oropharynx and the mandibular space (see Chapter 4). The laryngoscope blade is the tool that controls and maneuvers the tongue. Fundamental to successful laryngoscopy is the selection of a blade, curved or straight, that will be wide and long enough to capture the tongue during laryngoscopy, sweep it leftward and inferiorly into the mandibular space out of the visual field, and permit direct visualization of the airway. The larger flange of the curved Macintosh blade usually provides better tongue control than the thinner blade of the straight Miller
blade. Many laryngoscopists prefer a size 4 Macintosh blade for most emergency airways to assure adequate blade length. However, choice of a laryngoscope blade and the technique used to facilitate intubation is best guided by personal choice and experience. The literature suggests that straight blades improve laryngoscopic view (increased exposure of the vocal cords), whereas curved blades provide better intubating conditions (continuous visualization of the vocal cords during ETT passage). Using an ETI (bougie) improves intubation success rates with the straight-blade technique.

The laryngoscope should be held low on the handle, so the proximal end of the blade pushes into the thenar or hypothenar eminence of the left hand. This grip will encourage lifting from the shoulder, keeping the elbow low, and keeping the wrist stiff during laryngoscopy. The operator should be in an upright position with his or her arms and hands at a comfortable working height, rather than stooping or straining to reach the patient. The patient’s bed should be elevated and the operator should step back from the patient so that his or her back is relatively straight during laryngoscopy.

Optimal head and neck positioning for DL is often described as the “sniffing position”; lower cervical flexion and atlanto-occipital extension. The sniffing position attempts to align the oral,
pharyngeal, and laryngeal axes of the upper airway (Fig. 12-5). Absent contraindications, alignment of these axes is important for optimizing the laryngoscopic view. The appropriate degree of lower cervical flexion brings the external auditory meatus to the level of the sternal angle of Louis or anterior surface of the shoulder. In adult patients of normal body habitus, a 4- to 6-cm pad beneath the occiput usually suffices for this purpose. Alternatively, the operator can extend
and lift the head with his or her right hand during laryngoscopy to determine the optimal position empirically. The head can then be supported by an assistant standing on the right side of the patient while the operator intubates or performs external laryngeal manipulation. In morbidly obese patients, optimal positioning will often require a ramp to be constructed from linens or pads placed beneath the upper torso, shoulders, neck, and occiput in order to align the ear canal with the sternal angle of Louis (see Chapter 39, Fig. 39-1). Airway ramps are also commercially available for this purpose. In small children with a protuberant occiput, the torso may need to be raised to allow the external meatus to fall back to the desired plane (see Chapter 25, Fig. 25-2). Because of individual variations in anatomy, the optimal head and neck position is often unpredictable, and may require empiric adjustment during the intubation attempt. It is critically important that some means of adjusting the patient’s position be available before initiating the procedure. Understanding optimal head and neck positioning will help operators appreciate the difficulty of performing DL on trauma patients and others who must be intubated in a fixed position.

This is the standard technique used with both curved and straight blades.

This is an alternative technique that may be useful when standard DL is unexpectedly difficult because of prominent upper incisors, a large tongue, or limited mouth opening.

This is an alternative technique often used in neonates, infants, and small children using a straight blade, or in adults when other techniques are predicted to be difficult or have failed. There are two phases to this method: (1) Blind insertion of the tip of the laryngoscope blade into the esophagus, and (2) visualization of the glottis during withdrawal. The potential for esophageal and tracheal injury or regurgitation resulting from opening the upper esophageal sphincter during blind insertion of the blade has not been studied.

If the glottis is directly visualized, it is usually easy to pass a tube into the trachea. However, even with excellent glottic exposure, it is possible to block the line of sight with the ETT during the intubation attempt. This possibility can be minimized by inserting the tube from the extreme right-hand corner of the mouth while an assistant retracts the lip, and by keeping the tube below the line of site while advancing it toward the glottis, raising it over the posterior landmarks only during the terminal phase of insertion. Tube shape can also influence the ease of visualization during intubation. Using a malleable stylet to produce a straight tube with a single “hockey-stick” bend of <35° just proximal to the balloon facilitates cord visualization during passage, by keeping the tube out of the line of sight until it passes the cords (Fig. 12-9). As the tube approaches the depth of the glottis, it is raised up over the posterior landmarks and passed through the vocal cords. A banana-shaped tube tends to cross the visual axis twice in the course of insertion and may interfere with visual guidance during placement.